The present invention relates generally to electric machines and, in particular, to a stator winding for an electric machine having radial aligned partial wraps, wraps, and wrap sets. Electric machines, such as alternating current electric generators, alternators, or direct current electric motors are well known. Prior art alternators typically include a stator assembly and a rotor assembly disposed in an alternator housing. The stator assembly is mounted to the housing, or housings, and includes a generally cylindrically-shaped stator core having a plurality of slots formed therein. The rotor assembly includes a rotor attached to a generally cylindrical shaft that is rotatably mounted in the housing and is coaxial with the stator assembly. The stator assembly includes a plurality of wires wound thereon, forming windings. The stator windings are formed of slot segments that are located in the slots and end loop segments that connect two adjacent slot segments of each phase and are formed in a predetermined multi-phase (e.g. three or six) winding pattern in the slots of the stator core. The rotor assembly can be any type of rotor assembly, such as a “claw-pole” rotor assembly, which typically includes opposed poles as part of claw fingers that are positioned around an electrically charged rotor coil. The rotor coil produces a magnetic field in the claw fingers. As a prime mover, such as a steam turbine, a gas turbine, or a drive belt from an automotive internal combustion engine, rotates the rotor assembly, the magnetic field of the rotor assembly passes through the stator windings, inducing an alternating electrical current in the stator windings in a well known manner. The alternating electrical current is then routed from the alternator to a distribution system for consumption by electrical devices or, in the case of an automotive alternator, to a rectifier and then to a charging system for an automobile battery.
One type of device is a high slot fill stator, which is characterized by rectangular shaped conductors whose width, including any insulation, fits closely to the width, including any insulation, of the rectangular shaped core slots. High slot fill stators are advantageous because they are efficient and help produce more electrical power per winding than other types of prior art stators. These stators, however, are disadvantageous because the windings are typically interlaced, in which two wires for each phase are required to alternate outer and inner radial portions of each slot. This interlaced design requires an even number of conductors per slot because each phase must include two conductors or a multiple of two conductors. This is because one end loop segment connects the slot segment housed in an outer radial depth of the first slot to a slot segment housed in an inner radial depth of the second slot. This conductor leaves a void in the outer radial depth of the second slot, therefore a second conductor must connect the slot segment housed in an outer radial depth of the second slot to a slot segment housed in an inner radial depth of the third slot. These interlaced windings require either an interlacing process to interlace continuous conductors of all the phases prior to inserting the winding into the core or a connection process to individually connect U shaped hairpins that are axially inserted into the core. Therefore, in either case, the interlaced wind has disadvantageously increased the complexity of placing the winding to the stator. Also, because an even number of conductors is required per phase, the stator either must have an even number of electrical turns or an odd number of turns with a very complex connection scheme of parallel and series conductors.
Increasing the number of turns in an electrical machine's stator increases the generated voltage and therefore, the power output at low rotational speeds, but it also increases the inductance, and therefore, reduces the output at high rotational speeds. Therefore, choosing the optimal number of electrical turns for a given application changes the shape of the output vs. rotational speed curve. To create a stator winding having a plurality of electrical turns in each phase, the conductor must have a plurality of serially connected slot segments housed in each slot. One common method of serially connecting the slot segments is to utilize end loop segments to connect consecutive slot segments of one phase. The portion of a conductor that includes at least two end loop segments connecting at least three consecutive slot segments of one phase is defined as a partial wrap, utilized herein. A partial wrap that winds around a core for one substantial revolution is defined as a wrap, utilized herein. It may, however, be desirable for one or more wraps to terminate prior to completing one full revolution around the core, and therefore, the phrase substantial revolution, utilized herein, defines a pass around a core for at least half of a revolution around the core. For the cascade winding, each partial wrap or wrap of conductor connects slot segments which are located substantially in the same layer, or the same substantial radial distance from the central axis of the core. The end loop segments of the plurality of wraps must be nested such that the end loop segments of the wrap having slot segments housed substantially in one layer do not violate the space of other end loop segments of wraps of other phases with slot segments housed in the same layer as well as end loop segments of wraps having slot segments housed in radial adjacent layers. Furthermore, it is desirable to have a high slot-fill electrical machine that can easily be processed to have an odd number of electrical turns.
It is desirable, therefore, to provide a stator that meets the requirements of a high slot fill stator including a plurality of radial aligned partial wraps, wraps, and wrap sets and therefore a plurality of electrical turns and does not require an even number of conductors per slot.